Whisk together the sugar and cornstarch in a wide saucepan. Stir in the water and orange juice; bring to a boil over medium-high heat, whisking until thickened. Stir in the cherries and orange zest, return to a boil, then reduce heat, and simmer for 10 minutes. While the cherries are cooking, spoon the ice cream into serving bowls.
Remove the cherries from the heat, and stir in the cherry extract. Pour in the brandy, and ignite with a long lighter. Gently shake the pan until the blue flame has extinguished itself. Spoon the cherries over the bowls of ice cream.

Footnotes
Note on flambeing
The flames may get quite high when flambeing, so pay attention to anything flammable above and around where you ignite the cherries. When the initial large flame has died down, a small blue flame will continue to burn for several seconds. Shake or stir the cherries gently to expose more alcohol to the flame, being careful that they do not burn. The goal is to have the small, blue flame burn for as long as possible, thereby reducing the raw alcohol flavor, caramelizing the sugars, and entertaining your guests!